Which bone is responsible for connecting the leg to the upper body?

The pelvis is the bone responsible for connecting the leg to the upper body. It serves as a critical junction between the lower limbs and the spine. The pelvis is composed of several bones including the ilium, ischium, and pubis, which together form a shield-like structure that supports the upper body's weight while providing attachment points for the lower limbs. This functional connection allows for movement and stability in the hips and legs.

The hip itself, while important for the mobility of the leg, is part of the pelvis and does not serve as a singular bone that connects the leg to the upper body. The femur is the long bone in the thigh itself, and the sternum is a bone located in the chest, which does not connect the legs to the upper body at all. Hence, the pelvis is the most accurate answer here.